Demand exists in a variety of applications for materials that exhibit damping properties. In general, damping is the dissipation of mechanical energy from a system. Damping can be important in applications such as electronics, sound isolation, automotive and transportation, building and construction, household appliances, industrial equipment, firearms, healthcare and medical devices, and personal and/or sports protection.
The capacity of a material for damping is related to its peak temperature of the tangent of delta (Tan Delta Peak Temperature), which can be determined by dynamic mechanical analysis (DMA) as described, for example, by M. P. Sepe in “Thermal Analysis of Polymers”, Rapra Review Reports, Vol. 8, No. 11, 1997, which is incorporated herein by reference. The tangent of delta (Tan Delta) of a material is the ratio of its loss modulus (E″) to its storage modulus (E′). Consequently, as the value of Tan Delta increases, the response of the material is relatively more viscous than it is elastic, which thus provides greater damping. When graphically depicted against temperature, a Tan Delta curve includes a prominent peak at a particular temperature, which is the Tan Delta Peak Temperature and also can be representative of or comparable to the glass transition temperature (Tg) of the material. In general, a material with a Tan Delta Peak Temperature which is relatively nearer to an application temperature, such as at or above room temperature, will possess better damping properties than a material with a Tan Delta Peak Temperature which is relatively lower than the application temperature.
Demand also exists in a variety of applications for materials that exhibit low compression set. In general, compression set is the permanent deformation of a viscoelastic material after being subjected to a constant stress and an elevated temperature. Low compression set is desirable, for example, in sealing and gasket applications in various industries. Disadvantageously, however, conventional low compression set seals and gaskets made from crosslinked EPDM or silicone rubbers do not exhibit good damping together with low compression set.
Thermoplastic elastomers (TPEs), which are polymer materials that exhibit elasticity while remaining thermoplastic, can be used for damping applications and also can be used for low compression set applications. Thermoplastic elastomers can include styrenic block copolymers (SBC), thermoplastic vulcanizates (TPV), thermoplastic olefins (TPO), copolyesters (COPE), thermoplastic urethanes (TPU), copolyamides (COPA), and olefin block copolymers (OBC).
Some commercially available SBCs, such as HYBRAR 5127 available from Kuraray Co., Ltd., are known to exhibit vibration damping properties at room temperature. HYBRAR 5127 has a Tan Delta Peak Temperature that is reported to be 20° C. (i.e., about room temperature). HYBRAR 5127 can be formulated into conventional TPE compounds that exhibit effective room temperature damping, but typically only if the TPE compounds contain at least 40 weight percent of HYBRAR 5127. Using such a high level is economically disadvantageous because HYBRAR 5127 is a relatively expensive ingredient. Additionally, TPE compounds including HYBRAR 5127, which is a non-hydrogenated and relatively low molecular weight material, typically exhibit relatively poor UV/weathering stability, insufficient high temperature durability, and high (i.e., poor) compression set, which makes such TPE compounds unsuitable for applications that require good damping and low compression set, such as sealing and gasket applications.